Aging: what exactly happens?

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I managed to find an electronic copy of Briggs in a library I have access to, and browsing through it I found this description in the section on chemical maturation:
Briggs said:
Volatile fatty acids Beer conditioning temperature is very important in determining the excretion of C 4 to C 10 fatty acids. Synthesis of short chain fatty acids by yeast stops at the onset of maturation. C 8 fatty acid increases in concentration during fermentation and this is replaced in maturation by C 10 acid. Glycerides and phospholipids are synthesized during maturation and so there is a general trend for a reduction in volatile acids as ageing proceeds. This trend can be reversed if maturation is extended too far. There can then be a rise in the concentration of free fatty acids owing to the hydrolysis of reserve glycerides, with consequent adverse effects on flavour. If a high maturation temperature is maintained for too long then there can be a slow excretion of C 10 acid (capric acid), which has a flavour threshold of 10 mg/l and this is undesirable. Maturation is seldom controlled specifically from the viewpoint of controlling volatile fatty acids. Provided that the warm conditioning is not extended beyond the time needed to reduce the concentration of vicinal diketones, and cold storage is controlled to the time required for stabilization of haze precursors, there should not be a problem.
Anybody know anything about capric acid?
 
MalFet said:
I managed to find an electronic copy of Briggs in a library I have access to, and browsing through it I found this description in the section on chemical maturation:

Anybody know anything about capric acid?

Great post! This is the kind of stuff I was talking about
 
I managed to find an electronic copy of Briggs in a library I have access to, and browsing through it I found this description in the section on chemical maturation:

Anybody know anything about capric acid?

C10 fatty acid. Named after goats. Three guesses how it tastes.

NB: C6 (Caproic) and C8 (caprylic) are similarly named; C4 (butryic) is rancid butter.

This chart can help you keep track of your volatile alkanoic acids:

http://www.rsc.org/images/OPINION-STYLES-395_tcm18-83463.jpg
 
beerchemist said:
C10 fatty acid. Named after goats. Three guesses how it tastes.

NB: C6 (Caproic) and C8 (caprylic) are similarly named; C4 (butryic) is rancid butter.

This chart can help you keep track of your volatile alkanoic acids:

http://www.rsc.org/images/OPINION-STYLES-395_tcm18-83463.jpg

What a lovely array of flavors!

Any sense of what "too long" means? I've been trying to understand what happens when beer gets too old. Certainly, a lot of the changes are just oxidation, but "goaty" definitely describes something I've tasted before in stales beers before.
 
So I woke up this morning with a few thoughts.

I apologize for any role I played in elevating things yesterday. In reality, the conversation was going nowhere and I should have just moved on.

I did have a few more thoughts on subjects that were brought up yesterday. Most of this is conjecture on my part, so please don’t take this as fact (or anything right out of Briggs):

  • The term “starvation” may well apply to at least part of the yeast cake. I would think that newly flocculated cells do persist in some small degree of homeostatic metabolism (my educated guess) but, over time, they will go completely dormant. And I can see that this could be described as starvation. I have not seen it written that way before but I can see how it would apply.
  • I mentioned this before but I would think that there are more suspended yeast cells in the primary vessel than after transferring to a secondary vessel. I can see how equilibrium between residual sugar, suspended yeast cells and flocculated yeast cells would account for this. But this is just a guess.
  • I think that yeast cells metabolize molecules that can cause off flavors and do this after reaching FG in addition to before reaching FG. Briggs seems to support this.
  • If the second and third statements are true, this may explain why it is better to keep the beer on the yeast cake.
  • If I read things correctly, one of the links earlier includes Jamil mentioning that commercial brewers take the beer off the cake early. But, he suggests that this is to avoid autolysis as a result of the HUGE amount of weight that rests on the flocculated cells from the large volumes of water in commercial batches. And goes on to mention that at batch volumes in homebrewing this is unlikely to be a significant threat.
  • Even if 2, 3 and 4 are incorrect, there are still arguments for keeping beer on the yeast cake. Infection and oxidation. There is an, albeit small, risk of infection anytime the beer is manipulated. And it is almost impossible to avoid introducing a small amount of oxygen when racking. I have read about oxidation and its role in beer spoilage (cardboard flavor) but I have absolutely no idea how much racking would affect this. But, to me, if I’m not sure, it is better to avoid it.
  • Give enough time, keeping beer on the yeast cake will not result in cloudy beer any more than racking a beer to secondary will. Yeast will eventually settle either with time and/or low temperatures (including in the bottle). Racking to a secondary will probably do it faster and this is likely why homebrewers have done it for so long.
  • I have no issue with using non-traditional means to achieve better beer. I switched from tap water for a different reason and realized then that I didn’t like the idea of using campden tablets. However, I do use whirlfloc and even occasionally clarity ferm. How is that for being hypocritical?
Anyway, glad to see there have been a few new posts adding more info on the subject. Good stuff.
 
I managed to find an electronic copy of Briggs in a library I have access to, and browsing through it I found this description in the section on chemical maturation:

Anybody know anything about capric acid?

The thought that it is possible to condition too long at a higher temperature makes me wonder.

I had thought that the temperature for secondary fermentation was not so important. This seems to be saying otherwise. I guess I overlooked that in my reading. It's too bad there is no mention of what too long means or what too high a temperature would be.
 
ayoungrad said:
The thought that it is possible to condition too long at a higher temperature makes me wonder.

I had thought that the temperature for secondary fermentation was not so important. This seems to be saying otherwise. I guess I overlooked that in my reading. It's too bad there is no mention of what too long means or what too high a temperature would be.

I would think that length of time and max temperature are directly related to yeast strain.

However, I'm sure a rough guideline could be determined with some experimentation.

I also wonder if there is a quicker way to break down those fatty acids
 
I would think that length of time and max temperature are directly related to yeast strain.

However, I'm sure a rough guideline could be determined with some experimentation.

I also wonder if there is a quicker way to break down those fatty acids

Agreed.

It really sounds like maturation is a balancing act. Cleaning up several things and not going too long so that you end up creating different unfavorable flavors. Maybe this is why commercial breweries sometimes go the chemically-expediated maturation route so that there is less uncertainty.
 
Certainly yeast can starve, but I can't imagine "starvation" being a useful concept in a brewing context. Even under relatively non-hostile conditions, living things need energy to stave off entropy. Warm-blooded mammals with big brains need a lot and yeast need less, but all need something.

When preparing yeast for long-term storage, a lot of thought goes into maximizing food storage molecules like glycogen and trehalose. There are good reports of yeast living in well prepared mineral cultures at room temperature for up to 40 or 50 years. They would eventually die of course, but yeast are amazingly good at cycling through active and dormant phases.

It doesn't make sense to me to think of "starvation" as this dormant phase, but rather the point at which not even dormancy can be metabolically maintained. When considering an entire yeast population, I'm not sure colony-wide starvation is the relevant category for the scales of time we are dealing with.

My (possibly false) operating assumption has always been that the yeast cake (i.e., the inch of gunk at the bottom of the fermentor) is relatively inert. I think talk about "leaving the beer on the cake" has come about from the conflation of two different realizations:

* That previous concerns of yeast-cake autolysis are overstated.
* That yeast can be important in conditioning after active fermentation.

Somewhere along the line, people turned "yeast cake not evil" into "yeast cake necessary". Obviously, both "evil" and "necessary" are waaay overstating the actual effects of the cake, but I'm not aware of any real data on the matter looking into more nuanced effects. In any case, it'd be a good experiment, though I think everyone would say that the differences would be relatively subtle.

My real question now is about the control mechanisms for yeast population dynamics: growth, flocculation, etc. I've recently discovered that one of the University libraries I have access to has pretty much every major English brewing text I've ever heard of, but unfortunately only in an asinine drm format that requires me to read it in a Flash app. I'm going to see if I can pick through some of this and will report back.
 
Certainly yeast can starve, but I can't imagine "starvation" being a useful concept in a brewing context. Even under relatively non-hostile conditions, living things need energy to stave off entropy. Warm-blooded mammals with big brains need a lot and yeast need less, but all need something.

When preparing yeast for long-term storage, a lot of thought goes into maximizing food storage molecules like glycogen and trehalose. There are good reports of yeast living in well prepared mineral cultures at room temperature for up to 40 or 50 years. They would eventually die of course, but yeast are amazingly good at cycling through active and dormant phases.

It doesn't make sense to me to think of "starvation" as this dormant phase, but rather the point at which not even dormancy can be metabolically maintained. When considering an entire yeast population, I'm not sure colony-wide starvation is the relevant category for the scales of time we are dealing with.

My (possibly false) operating assumption has always been that the yeast cake (i.e., the inch of gunk at the bottom of the fermentor) is relatively inert. I think talk about "leaving the beer on the cake" has come about from the conflation of two different realizations:

* That previous concerns of yeast-cake autolysis are overstated.
* That yeast can be important in conditioning after active fermentation.

Somewhere along the line, people turned "yeast cake not evil" into "yeast cake necessary". Obviously, both "evil" and "necessary" are waaay overstating the actual effects of the cake, but I'm not aware of any real data on the matter looking into more nuanced effects. In any case, it'd be a good experiment, though I think everyone would say that the differences would be relatively subtle.

My real question now is about the control mechanisms for yeast population dynamics: growth, flocculation, etc. I've recently discovered that one of the University libraries I have access to has pretty much every major English brewing text I've ever heard of, but unfortunately only in an asinine drm format that requires me to read it in a Flash app. I'm going to see if I can pick through some of this and will report back.

All good points. IMHO there is probably a little more "cleaning-up" that occurs on the cake from more yeast, but you are probably right that the difference is minimal.

It sounds like you have your work cut out for you with all the new info you found.

FWIW, and you may have already seen this, Briggs has quite a bit about yeast flocculation, metabolism, life cycyle and growth patterns. But in skimming back through the book yesterday I did not find anything specific about activity of flocculated yeast.

Let us know if you find anything interesting.
 
Good to see this back on track.

Originally Posted by Briggs
Volatile fatty acids Beer conditioning temperature is very important in determining the excretion of C 4 to C 10 fatty acids. Synthesis of short chain fatty acids by yeast stops at the onset of maturation. C 8 fatty acid increases in concentration during fermentation and this is replaced in maturation by C 10 acid. Glycerides and phospholipids are synthesized during maturation and so there is a general trend for a reduction in volatile acids as ageing proceeds. This trend can be reversed if maturation is extended too far. There can then be a rise in the concentration of free fatty acids owing to the hydrolysis of reserve glycerides, with consequent adverse effects on flavour. If a high maturation temperature is maintained for too long then there can be a slow excretion of C 10 acid (capric acid), which has a flavour threshold of 10 mg/l and this is undesirable. Maturation is seldom controlled specifically from the viewpoint of controlling volatile fatty acids. Provided that the warm conditioning is not extended beyond the time needed to reduce the concentration of vicinal diketones, and cold storage is controlled to the time required for stabilization of haze precursors, there should not be a problem.

Great find!!!! This might just answer something I've been wondering about. The real myth about autolysis is that it leads to rank off flavors. Autolysis of yeast starts to occur once stationary phase begins. Biological fact. It may not be happening to a large extent, but it is going on. I personally believe this leads to a yeasty/bready flavor, much like it does in wines aged on the lees (yeast cake). Good for some styles, not for others. Now Capric acid, this is very stinky stuff indeed. I can easily see where this could smell like burnt rubber and the other foul spelling odors that are attributed to autolysis - incorrectly. These volatile fatty acids could very well be what people are smelling.

Like I said before, there are plenty of things that are different between large commercial brewing versus homebrewing. However the biochemical reactions are going to be the same. What does change is the relative proportions of each of these reactions and the temperatures they occur at, but they are all going on. There is the potential for the reactions mentioned in the quote to occur during homebrewing, same as in commercial brewing - if the beer is aged too long, too warm, etc.

The warmer the yeast are after fermentation has occurred, the more "active" they will be, and the more likely they are to use up any stored food reserves, resulting in these nasty fatty acids as mentioned in the quoted text.

With respect to temperature during a secondary, it is not as important as during primary, but it is still important. Too warm, and it appears as you could get attacked by goats! I suspect that as long as it is not too warm, the yeast will be dormant enough to not start breaking down their food reserves.

In terms of a faster way to break down the fatty acids (and prevent their later formation), the best way is to make sure you have happy yeast (temp, pitch rate, aeration, etc.)

Somewhere along the line, people turned "yeast cake not evil" into "yeast cake necessary". Obviously, both "evil" and "necessary" are waaay overstating the actual effects of the cake, but I'm not aware of any real data on the matter looking into more nuanced effects. In any case, it'd be a good experiment, though I think everyone would say that the differences would be relatively subtle.

Ah, the beauty of the internet. This pretty much nails it. Information of all kinds, spread at the spread of light. One could easily reverse these and swap out "yeast cake", switch the NOT and replace it with "protein rest" (not needed = evil)

One issue we haven't really addressed, and one I see rarely mentioned is the role of extracellular proteases and loss of foam. Lots of people are reporting that their long primary only beers are tasting great. Great! However, I haven't heard many reports on how the head is on these beers. There is literature out there showing that the extracellular proteases do degrade foam stabilizing proteins in beer. This would suggest that the quicker the fermentation and the shorter the contact with the yeast, the better - with respect to head formation. My own personal experience though with kegged beer is that I seem to get better head towards the end of the keg. There is some yeast in the kegs, but not lots. Now I haven't really paid attention to this and need to be more observant. It might just be that with my normal set and forget, force carbing, while it may appear to reach equilibrium in a week (ie fully carbed), there are other things going on and it might actually take several weeks to really reach equilibrium (maximum head potential). Maybe I just haven't been observant enough and just hadn't noticed the head got better earlier and wasn't realizing it until later. I compare it to the first pints of a keg, and those are always sampled a bit early. :eek: I'd be curious to hear from some bottlers. Say, "measure" (rate it, may be good enough) the foam over the course of 8 weeks, starting 2 weeks after bottling.
 
Great find!!!! This might just answer something I've been wondering about. The real myth about autolysis is that it leads to rank off flavors.

Yeah, when I read that, the first thing I thought was also..."this sounds a lot like how people talk about autolysis". It has the advantage too of operating on some of the same mechanisms.

It is certainly a positive thing that people have largely gotten over the idea that a couple extra weeks on the yeast will lead to Jonestown-esque mass autolyzing, but I don't think many people understand (myself definitely included) what dormancy means, exactly, for beer production.

Anecdotally, 85% of my beers get bottled after about 2 weeks, but occasionally, due to either challenging yeast or sheer laziness, I'll go as long as 6-8 weeks. I haven't observed any particular changes in head retention, and I have been watching for it. This is a long way from a controlled trial, though.

How would you explain better head retention towards the end in terms of protease? My initial impulse would be to attribute that observation to physical settling (and thus less nucleation), but that would be just a guess. I'm curious about alternatives.
 
I hope this isn't too far off topic since it's not strictly about aging, but we've mostly been talking about yeast metabolism anyway. In any case, if this is a derail, o4_srt, let me know and I'll start a different thread.

Here's an interesting quote from Briggs (p. 456) on ester production that I just found while trying to answer somebody else's question.
The synthesis of esters requires the expenditure of metabolic energy suggesting that ester formation must fulfil an important metabolic role. It may be a mechanism for regulating the ratio of acyl-CoA to free CoA (Thurston et al., 1981). Peak ester concentrations are reached after the formation of higher alcohols has ceased (Fig. 12.1). Rates of ester synthesis are maximal at the mid-point of fermentation coinciding with the cessation of lipid synthesis. Thus, when acetyl-CoA cannot be utilized by lipid synthesis, the formation of esters provides an alternative use for this substrate. Intermediates of lipid biosynthesis influence ester formation. Supplementation of worts with the unsaturated fatty acid, linoleic acid (50 mgl􏰀1) causes a dramatic decrease in ester formation (Thurston et al., 1982). It was suggested that this effect was due to inhibition of alcohol acyl- transferase by unsaturated fatty acids. This effect has been confirmed by others (Yoshioka and Hashimoto, 1982a, b, 1984) and led to the proposal that ester and lipid syntheses are inversely correlated. This is supported by the observation that increasing oxygen supply to wort tends to decrease ester synthesis. In this case, oxygen promotes the synthesis of unsaturated fatty acids, which in turn reduces the activity of alcohol acyltransferase.

I know lipid synthesis is a big part of population growth, but how does this play out once population levels have more or less hit equilibrium?
 
So I woke up this morning with a few thoughts.

I apologize for any role I played in elevating things yesterday. In reality, the conversation was going nowhere and I should have just moved on.

I did have a few more thoughts on subjects that were brought up yesterday. Most of this is conjecture on my part, so please don’t take this as fact (or anything right out of Briggs):

  • The term “starvation” may well apply to at least part of the yeast cake. I would think that newly flocculated cells do persist in some small degree of homeostatic metabolism (my educated guess) but, over time, they will go completely dormant. And I can see that this could be described as starvation. I have not seen it written that way before but I can see how it would apply.
  • I mentioned this before but I would think that there are more suspended yeast cells in the primary vessel than after transferring to a secondary vessel. I can see how equilibrium between residual sugar, suspended yeast cells and flocculated yeast cells would account for this. But this is just a guess.
  • I think that yeast cells metabolize molecules that can cause off flavors and do this after reaching FG in addition to before reaching FG. Briggs seems to support this.
  • If the second and third statements are true, this may explain why it is better to keep the beer on the yeast cake.
  • If I read things correctly, one of the links earlier includes Jamil mentioning that commercial brewers take the beer off the cake early. But, he suggests that this is to avoid autolysis as a result of the HUGE amount of weight that rests on the flocculated cells from the large volumes of water in commercial batches. And goes on to mention that at batch volumes in homebrewing this is unlikely to be a significant threat.
  • Even if 2, 3 and 4 are incorrect, there are still arguments for keeping beer on the yeast cake. Infection and oxidation. There is an, albeit small, risk of infection anytime the beer is manipulated. And it is almost impossible to avoid introducing a small amount of oxygen when racking. I have read about oxidation and its role in beer spoilage (cardboard flavor) but I have absolutely no idea how much racking would affect this. But, to me, if I’m not sure, it is better to avoid it.
  • Give enough time, keeping beer on the yeast cake will not result in cloudy beer any more than racking a beer to secondary will. Yeast will eventually settle either with time and/or low temperatures (including in the bottle). Racking to a secondary will probably do it faster and this is likely why homebrewers have done it for so long.
  • I have no issue with using non-traditional means to achieve better beer. I switched from tap water for a different reason and realized then that I didn’t like the idea of using campden tablets. However, I do use whirlfloc and even occasionally clarity ferm. How is that for being hypocritical?
Anyway, glad to see there have been a few new posts adding more info on the subject. Good stuff.

Thanks, that was a great post; I also apologize for not helping much to avoid the thread going downhill as it did yesterday.

Briggs is a great source just like some folks here and other books. I have read pieces and bits of all major brewing books and now I have access to Briggs too. Look forward to read it.

I just see things in a different perspective and I was hoping some of you were more open to it. I don't expect everything in books to be backed-up by a published scientific experiment. Nevertheless, from a cell biology standpoint, I have been intrigued by what authors say regarding yeast activity in fully fermented vessels despite of the paucity of energy source.

Since their observations seemed to be based on long term knowledge (experience), I thought it would been nice if there was an actual experiment that proves the breakdown of molecules that are known to result in off-flavors by yeast after maximum attenuation has been reached. There is no such experiment published though. That's why I have to rely in general biology and metabolism of S. cerevisiae in a different, but highly funded context to try making sense of what/how/why could possibly happen. The yeast go dormant after sugar content is depleted, there is no question about it, and there is plenty of high quality research describing the changes in metabolism that accompany dormancy, likely a process to protect against death and autolysis. There are many aging processes with distilled alcoholic beverages that have nothing to do with yeast contact either. So, I still think that a good deal of the benefits of aging well accepted and widespread in the brewing community is possibly resultant from yeast-independent mechanisms. I just don't want to persist on that anymore.
 
Autolysis of yeast starts to occur once stationary phase begins. Biological fact.

No. Autolysis begins with the death of the cell. A healthy yeast cell enters the stationary phase to endure a prolonged period of less than ideal living conditions. A yeast cell can die at any time and undergo autolysis, but the stationary phase does not equal death.

Temperature, pH, and alcohol content all play a role in the rate of autolysis.

I know it's concerning wine, but this is a pretty good paper.
 
No. Autolysis begins with the death of the cell. A healthy yeast cell enters the stationary phase to endure a prolonged period of less than ideal living conditions. A yeast cell can die at any time and undergo autolysis, but the stationary phase does not equal death.

Temperature, pH, and alcohol content all play a role in the rate of autolysis.

I know it's concerning wine, but this is a pretty good paper.

I'll let pjj2ba speak for himself, but I didn't take anything in his post to suggest that he thinks that an individual cell necessarily starts autolyzing at the beginning of it's stationary phase, but that a population of yeast starts exhibiting autolzing cells at that point.
 
No. Autolysis begins with the death of the cell. A healthy yeast cell enters the stationary phase to endure a prolonged period of less than ideal living conditions. A yeast cell can die at any time and undergo autolysis, but the stationary phase does not equal death.

Temperature, pH, and alcohol content all play a role in the rate of autolysis.

Of course it begins with the death of the cell! That goes without saying. I did not mean to imply that once a culture enters stationary phase that the cells will die. Of course not! However, not much cell death is occuring prior to stationary phase. Once the culture reaches stationary phase, most of the yeast will just kinda hang out in limbo, but there will be some yeast that will die and then autolyze.

It may not be happening to a large extent, but it is going on
I had hoped this was sufficient to suggest that only a small number of the yeast are dying and autolyzing, and that most are just hanging out

The point is, once fermentation is complete, there will be some amount of yeast undergoing autolysis (after dying first). This is not going to create a bunch of nasty flavors in one's beer. In some styles they can be quite nice in fact. The myth is about autolysis and off-flavors, not about autolysis not occuring
 
Autolysis occurs in your starter. Autolysis happens during fermentation. Autolysis is in every bottle of naturally carbonated brew.

I'm not sure what the death rate of yeast is at any given point of its life cylcle.
True, autolysis is more of a concern while beer is sitting on the yeast cake. But, that is more a function of the number of organisms than the fact that they are in a given phase.

My issue is the statement that it is a fact that autolysis is a result of entering the stationary phase. It is not.
 
Of course it begins with the death of the cell! That goes without saying. I did not mean to imply that once a culture enters stationary phase that the cells will die. Of course not! However, not much cell death is occuring prior to stationary phase. Once the culture reaches stationary phase, most of the yeast will just kinda hang out in limbo, but there will be some yeast that will die and then autolyze.

I had hoped this was sufficient to suggest that only a small number of the yeast are dying and autolyzing, and that most are just hanging out

The point is, once fermentation is complete, there will be some amount of yeast undergoing autolysis (after dying first). This is not going to create a bunch of nasty flavors in one's beer. In some styles they can be quite nice in fact. The myth is about autolysis and off-flavors, not about autolysis not occuring

Yep, that's what I understood from your post too. No autolysis before stationary phase.

S. cerevisiae though do a good deal of metabolic adaptations and genomic arrangement to keep integrity and preventing going into cell death once in the dormant stage. This is a huge area of research outside the brewing world because it helps scientists to understand how pathogenic fungi can resist nutrient-poor environments and also help other groups of scientists to understand the reasons behind prolonged lifespan. It's a fascinating subject.

Some of the brewing authors out there, like JP, say that autolysis is minor or a simply a no-issue with modern yeast cells available for homebrewing nowadays. That has actually some scientific back-up, not specifically in a homebrewing setup unfortunately, but there are several works out there proving that yeasts of the same genus are incredibly resistant to autolysis even under prolonged periods of dormancy.

I’m not sure how much autolysis would be necessary to give off-flavors to a 5-gal batch, but I bet any significant amount would likely ruin it.
 
I guess I'm thinking of the stationary phase as it pertains to an individual, rather than a population.

The taste imparted by autolysis does vary from a pleasant bready, yeast taste, to meaty, or, if its really bad, rubbery.
 
My issue is the statement that it is a fact that autolysis is a result of entering the stationary phase. It is not.

Yes, I'm thinking in terms of the whole culture

I didn't mean to imply that cells die because they enter stationary phase. Cells will die during all stages of the culture cycle. It is more likely to occur during stationary phase than any other phase though. Certainly not because they are in stationary phase and certainly not the cause of stationary phase.

All I want to say is :

A) autolysis is a fact.

B) It is more likely to occur during stationary phase
 
I think a lot of the issues homebrewers have when they think of yeast is that they believe it works as a community, not billions of individual organisms.

I usually approach it from the opposing camp. Each little critter reacting to it's environment. The conditions are similar, but the reaction and timing differ.

I just didn't want someone to come across stationary phase = autolysis and misinterpret it to mean that they need rack off the primary ASAP.
 
So I started reading a little in Birggs about flocculation and came across pages 377-8. Indyking might find it interesting that they use the term starvation...

"Commonly, flocculation occurs only when sources of fermentable sugars are exhausted. It has been suggested (Iserentant 1996) that under such starvation conditions the ability to form flocs may represent a stress response. Thus, flocs provide a sheltered environment where the chance of survival of the population is enhanced. Disaggregation of flocs occurs if the cells are again exposed to a source of fermentable sugar. The precise mechanism by which flocculation occurs is controversial… in brewing, flocculation occurs toward the end of primary fermentation…”

And it mentions inhibitors of flocculation to include glucose, mannose and maltose.

It does not seem to indicate that yeast cells become dormant when they flocculate. Flocculation seems to only be an adaptation to low/absent sugars but, at least in my interpretation so far, the flocculated yeast are still metabolizing.
 
Thanks to the civil among you for an informative thread! The most useful thing I got out of it was learning that the book Briggs' Brewing: Science and Practice exists, and then I was able to save myself several hundred dollars by tracking down a free PDF of the ENTIRE BOOK. Legality is questionable so I'm not going to link anything, but folks, it's out there!
 
Thanks to the civil among you for an informative thread! The most useful thing I got out of it was learning that the book Briggs' Brewing: Science and Practice exists, and then I was able to save myself several hundred dollars by tracking down a free PDF of the ENTIRE BOOK. Legality is questionable so I'm not going to link anything, but folks, it's out there!

You can get almost any book, music or video for free on the internet as long as you know how to convert rar files. All available and almost all completely illegal. I'm not saying this just becuase I bought the book. I saw the files on the internet before I bought the book but I wanted the actual book and I know about rar files.

But, yes, I agree, the info there is really great.
 
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